A number of electrical devices are located in a nuclear reactor building and require electric connection wires and cables. Such devices include measuring sensors, particularly sensors for measuring the position of the control clusters in the reactor core and thermo-couples for measuring the temperature of the core, and mechanisms for actuating the neutron absorption clusters for controlling and stopping the core. The cables are numerous and cumbersome, in particular above the cover of the reactor vessel. By way of example, for a nuclear reactor with four loops, the number of control and shutdown clusters may be as high as seventy-three and the number of thermo-couples as high as fifty-two. For each control cluster, cable is required for powering the cluster actuating mechanism and a cable for the sensor measuring the position of the cluster; each thermo-couple is connected to a cable. That makes a total of one hundred and ninety-eight cables.
To date, the cables have been disposed as follows: each cable has a first section connecting the electric device and a fixed connector installed above the cover. A second section extends from the fixed connector to another fixed connector installed on a connector plate remote from the reactor; all second sections of the cables are distributed in two half rings and then extend from the reactor as a single harness supported by a bridge disposed between the reactor and the plate installed at a distance therefrom.
Such a cabling installation has disadvantages. Positioning the cables is a long and delicate operation since a single section extends from a fixed connector situated above the cover to the plate situated at a distance from the reactor, and is consequently very long and difficult to handle. The diameter of the section may be such that it cannot easily be bent, and the small space available above the cover cannot accomodate an excess cable length; the length of each cable is therefore adjusted on the spot during installation thereof, the removable connectors situated at the ends of the cables are consequently mounted on the spot, under difficult conditions.
Once installed, the cable has further drawbacks: for removing the cover from the reactor the cables must be disconnected from the plate remote from the core and the bridge must be raised along with the cables which it supports.
Furthermore, changing a cable during the lifetime of the reactor is a difficult operation since the large number of cables means that the bridge supports several layers of cables: handling of the cables in the lower part of the harness which extends across the bridge is difficult in the hostile environment due to radioactivity from the core.
The difficulties are still greater when the number of sensors measuring the position of the clusters is increased to achieve redundancy (for example to four) for reliability. This means installing four sensors which transmit the same information to four different processing systems. In this case, and to comply with the safety standards, the electric power supplies for these measuring systems must be different in origin and spatially separated. Similarly, the paths for the transmission cables must be different and minimum distances, of about 300 mm if these paths are open, are required between the paths followed by these cables. Referring to the above example, with redundant sensors for measuring the position of the clusters, the number of cables for measuring the positions of the clusters, which was seventy-three, now becomes two hundred and ninety-two. Added to the cable supplying power to the cluster actuating mechanisms and to those carrying temperature signals from thermocouples, a total of four hundred and seventeen cables must be installed above the cover. Taking into account the minimum distances imposed by installation regulations, the volume required for the cables is appreciably greater than the volume of cables used to date since the amount of cables is about three times greater than that used at present.
There is consequently a need for a wiring arrangement making it possible to increase the number of sensors measuring the position of the control clusters so that they may be redundant and free of the above-mentioned disadvantages.